That’s a great instinct—depth is one of the biggest factors in successful nymphing, and a lot of anglers don’t even realize they’re fishing too high in the water column. Here’s how to diagnose the problem and make sure your flies are in the zone:

• Are you making contact with the bottom? A good indicator that your nymphs are deep enough is if you’re occasionally ticking the riverbed. You don’t want to snag up every cast, but if you never feel the occasional bump, your flies are likely riding too high.
• Check your leader length. If you’re fishing an indicator rig, your leader should be at least 1.5x the depth of the water. So if you’re fishing a 4-foot deep run, your indicator should be set 6 feet above your flies. If you’re tightlining, extend your tippet a bit and use a heavier point fly to help your rig sink faster.
• Adjust your weight. The quickest way to get deeper is to add a bit more weight—either by using a heavier fly or adding split shot. If you’re fishing a tandem rig, try using a tungsten beadhead fly on the bottom to help pull the whole setup down.
• Watch your drift speed. If your flies are moving as fast as the surface current, they’re too high in the column. Properly weighted nymphs should drift slightly slower than the water on top because they’re near the riverbed, where the current is weaker.
• Make the first drift count. The first cast into a good-looking run should be weighted to get deep right away. A lot of people fish too light at first and only get down after a few drifts—by then, they’ve already spooked fish. Start heavy and adjust if needed.

If you try these adjustments and start hitting bottom more often (but not constantly snagging), you’ll know your flies are right where they need to be. Hope this helps—tight lines!